1. Field of the Invention
The present invention relates to a developing unit for use in an image forming apparatus such as a laser printer, a copier, facsimile machine or the like and, in particular, relates to a toner replenishing device for replenishing, as required, a developing hopper as a part of the developing unit, with the toner for image development.
2. Description of the Related Art
An image forming apparatus such as a laser printer, a copier, a facsimile machine, or the like, utilizing an electrophotographic technique, has an image forming portion for forming a desired image on a sheet for recording. In this image forming portion, the surface of a photosensitive member as an image bearer is uniformly electrified with charges of a particular polarity and then is illuminated with an optical image to form a static latent image corresponding to the image. For the purpose of visualizing this static latent image, the image forming portion includes a developing unit and other components. The developing unit is composed of developer hopper holding a developer and having a developing roller and the like for supplying the developer to the developing position where the developing roller opposes the photosensitive member. Further, since the toner in the developing hopper is consumed, the developing unit is provided, adjacent to the developing hopper, with a toner replenishing device for replenishing the developing hopper, if necessary, with the toner which is a developer.
In the developing unit described above, if the toner reserve container for replenishing the developing hopper with the developer is arranged on the top, the developing unit would be bulky as to its height and hence a waste space would arise inside the image forming apparatus, thus making the whole image forming apparatus bulky. For this reason, the toner reserve container is horizontally arranged adjacent to the developing hopper to reduce the height of the developing unit, thus making the developing unit into a low profile and at the same time making an image forming apparatus as a whole compact by eliminating the unnecessary space which would arise inside the image forming apparatus.
For example, an example of such a developing unit is disclosed in Japanese Patent Application Laid-Open Hei 10 No. 123815. A toner replenishing device has a rotatable toner conveying unit for agitating the toner and conveying the toner at the same time in a toner reserve container (toner hopper) for reserving the toner. This toner conveying unit has the function of securing the performance of conveying the toner and the function of preventing a degradation in the toner (flocculation or the like) by agitating the toner.
The toner conveying unit described above is conventionally constituted by an agitator which is a rotary member usually formed of a considerably hard material (metal, resin or the like), and firmly formed like a ladder, as disclosed in Japanese Patent Application Laid-Open Hei 10 No. 301377, for example, and a flexible conveying sheet provided at an end portion of the agitator so as to convey the toner.
As described above, since the toner reserve container is provided with the toner conveying unit made up of the agitator and the conveying sheet, the toner stored in the toner reserve container is completely conveyed without being stagnated by the above-mentioned toner conveying unit with sufficient conveyance even if the amount of the toner becomes smaller. For example, in the toner conveying unit disclosed in Japanese Patent Application Laid-Open Hei 6 No. 236110, an elastic sheet (corresponding to the conveying sheet) is provided at the tip of the agitator. The elastic sheet is put into sliding contact with the inside of the toner reserve container by rotating the agitator to sufficiently agitate and convey the toner having the tendency to accumulate on the bottom and the like. Therefore, even if the amount of toner becomes smaller, the performance of conveying the toner can be sufficiently secured and problems such as toner stagnation and the like are not presented and hence the toner can be effectively used.
Also, in the toner conveying unit disclosed in Japanese Patent Application Laid-Open Hei 10 No.301377 a ladder-shaped toner agitator provided with a rectangular film (corresponding to the conveying sheet) produces the same effect as is disclosed in the Japanese Patent Application Laid-Open Hei 6 No.236110.
Further, in Japanese Patent Application Laid-Open Hei 10 No.123815 proposed by the present inventor is also disclosed a conveying unit including an agitator and a film-shaped conveying sheet fixed to the agitator, wherein the tip end portion of the conveying sheet is in sliding contact with the inside of a toner reserve container to secure toner conveyance to stably convey the toner. In this conveying sheet, in order to further secure the toner conveyance, the tip end of the conveying sheet is bent in the rotational direction to increase the toner conveyance.
In the configuration of the conventional toner replenishing device described above, the agitator arranged in the toner reserve container is provided with the conveying sheet made of a flexible sheet or film for sufficiently securing toner conveyance even when the quantity of toner becomes smaller.
However, if the toner storage capacity of the toner reserve container is large, the toner stored in the toner reserve container can not completely be conveyed unless the conveying sheet fixed to the agitator is elongated. In this case, the strength and rigidity of the conveying sheet or the like is a big problem. For example, if a large amount of toner is stored in the toner reserve container, the conveying sheet is largely deformed to reduce the toner conveyance. To overcome the problem, it is recommended that a conveying sheet having sufficient rigidity be used, but because the conveying sheet is in sliding contact with the toner reserve container, it loses flexibility and can not be largely curved, thereby applying large load to a driving motor and to the conveying sheet itself, resulting its shorter life.
Further, the above conveying sheet is made of, for example, a polyethylene terephthalate (PET) film or a polyester film or the like so that it has good flexibility and has a tolerance against deformation and curving. For this reason, if the conveying sheet is repeatedly curved and deformed, the conveying sheet may be plastically deformed and bent and unable to reset its curvature and deformation and hence lose its toner conveying performance and its toner agitating performance.
Then, in Japanese Patent Application Laid-Open Hei 10 No. 301377 is disclosed a technique for reducing the force applied to a resin conveying sheet (film) during its rotation by making a plurality of holes in the conveying sheet fixed to an agitator. This technique can prevent the toner from applying a rotational load to the conveying sheet and, at the same time, can prevent a decrease in life caused by deformation or the like to some extent, even if the amount of toner is large.
However, it is thought that the toner conveying performance is reduced because the rigidity of the film is reduced by many holes made in the film, as described above. Also, if a plurality of holes are only made, the amount of toner conveyed by the conveying sheet is reduced as well. In particular, if many holes are formed in the portion for conveying the toner, they tend to reduce the total amount of conveyed toner.
Further, since the holes are formed uniformly in the whole area of the conveying sheet, the toner conveying performance is reduced at the tip end of the conveying sheet, whereby part of toner is left in the toner reserve container and the toner can not completely effectively conveyed.
In view of the above problems, it is an object of the present invention to provide a toner replenishing device capable of making effective use of a toner stored in a toner reserve container and always securing a stable toner conveying performance and the sufficient amount of conveyed toner.
It is another object of the present invention to provide a toner replenishing device capable of securing a sufficient toner conveying performance only by adding a very simple configuration thereto.
In order to accomplish the above objects, a toner replenishing device according to the first invention is a toner replenishing device including a toner conveying unit for agitating and conveying a toner stored in a toner reserve container, wherein the toner conveying unit includes an agitator for rotating the toner stored in the toner reserve container and a conveying sheet fixed to the one end portion of the agitator and conveying the stored toner, wherein the conveying sheet has a plurality of slits.
Since the conveying sheet has the above configuration, even if the conveying sheet having large rigidity and strength and relatively large thickness for a conveying sheet is selected, if the above-mentioned slits are formed in the conveying sheet, the slits absorb the toner pressure applied to the conveying sheet and the load applied thereto when its tip end contacts the toner reserve container to make the conveying sheet be easily curved and deformed. For this reason, the slits can prevent an increase in torque when the conveying sheet is rotated and can make the conveying sheet secure toner conveying performance by sufficient rigidity and strength.
In the toner replenishing device according to the first invention characterized by the above-mentioned configuration, the slits are formed in the direction of the extension of the conveying sheet from the base end portion thereof where the conveying sheet is fixed to the agitator to the tip end side of the conveying sheet. Since the slits are formed in the radial direction with respect to the rotation of the agitator, they do not largely reduce the rigidity of the conveying sheet but easily deform the conveying sheet, whereby the conveying sheet can sufficiently secure the toner conveying performance and keep it throughout a long period of use.
In the toner replenishing device according to the first invention characterized by the above-mentioned configuration, the slits are formed close to the end portion where the conveying sheet is fixed to the agitator. Therefore, the conveying sheet for conveying the toner can sufficiently secure the rigidity at its tip end side and hence can stably convey the toner. In other words, since the slits are formed in the conveying sheet close to the end portion where the conveying sheet is fixed to the agitator, the conveying sheet is deformed in the portion where the slits are formed to absorb the toner pressure and the other load at the portion, thereby securing stable toner conveying performance even if it is used for a long time.
Also, in the toner replenishing device according to the first invention characterized by the above-mentioned configuration, if the slits are formed at pitches which become gradually larger from the center portion to both end portions in the direction of the rotary shaft of the agitator, the conveying sheet can secure the rigidity at its both end portions in the direction of the rotary shaft of the agitator. In other words, in the toner conveyance by the conveying sheet, the toner conveying performance tends to be reduced in both end portions as compared with the center portion. That is, the conveying sheet is largely deformed at both end portions to make the distribution of the amount of conveyed toner nonuniform in the direction of the rotary shaft. In order to correct this, if the slits are formed at pitches which become gradually larger from the center portion to both end portions, they can secure the rigidity of the conveying sheet and make the distribution of toner conveyance nearly uniform as a whole in the direction of the rotary shaft.
Further, if the slits are made gradually smaller from the center portion to both end portions in the direction of the rotary shaft of the agitator, it is possible to make the distribution of toner conveyance nearly uniform as a whole in the direction of the rotary shaft, as described above.
Also, a toner replenishing device according to the second invention to accomplish the above-mentioned objects is a toner replenishing device including a toner conveying unit for agitating and conveying a toner stored in a toner reserve container, wherein the toner conveying unit comprises an agitator for rotating the toner stored in the toner reserve container and a conveying sheet fixed to one end portion of and conveying the stored toner, wherein the conveying sheet has a plurality of openings formed close to the end portion where the conveying sheet is fixed to the agitator.
Even if a film or the like having a larger thickness for a conveying sheet is used as a conveying sheet, if it has a plurality of openings like this configuration, it can be easily deformed so as to absorb the toner pressure and the load applied thereto when its tip end contacts the inside wall of the toner reserve container and can stably convey the toner for a long time. In this case, since the openings are formed not in the tip end portion of the conveying sheet but in the portion close to the end portion thereof where the conveying sheet is fixed to the agitator, it is possible to eliminate the stagnation of the toner in the toner reserve container and to completely convey the toner. In addition, the openings can sufficiently secure the toner agitating performance and largely reduce the load applied to the conveying sheet to make it possible for the conveying sheet to be used for a long time.
In the toner replenishing device according to the second invention characterized by the above-mentioned configuration, if the plurality of openings described above have the same shape and the same opening area and are formed at pitches which become gradually larger from the center portion to both end portions in the direction of the rotary shaft of the agitator, the conveying sheet can secure rigidity at both ends in the direction of the rotary shaft. In other words, in the toner conveyance by the conveying sheet, the toner conveying performance tends to be reduced in both end portions as compared with the center portion. Therefore, the conveying sheet is largely deformed at both end portions to make the distribution of the amount of conveyed toner nonuniform in the direction of the rotary shaft. In order to correct this, if the openings are formed at pitches which become gradually larger from the center portion to both end portions, they can secure the rigidity of the conveying sheet and make the distribution of toner conveyance nearly uniform as a whole in the direction of the rotary shaft.
Further, if the openings are made gradually smaller in the opening area from the center portion to both end portions in the direction of the rotary shaft of the agitator, it is possible to make the distribution of toner conveyance nearly uniform as a whole in the direction of the rotary shaft, as described above.
Here, when the openings are formed, as shown in FIGS. 7C and 7D, for example, the number of openings is decreased in the mounting end portion where the conveying sheet is fixed to the agitator and is increased in the tip end side. Further, as shown in FIGS. 8A to 8C, in the plurality of openings, the area of the opening close to the tip end side is larger than that close to the mounting end portion. Forming the openings in this manner is effective in reducing the amount of toner scooped up by the openings of the conveying sheet having an object to convey the toner and in reducing the deformation of the conveying sheet by the toner scooped up near the tip end and in securing stable, sufficient toner conveyance. Therefore, if the plurality of openings are formed in such a way that the openings are increased in area as they get close to the tip end side from the mounting end portion where the conveying sheet is fixed to the agitator, as described above, they are useful for securing the toner conveyance.
As for the positions of the respective slits or openings in accordance with the first and second invention described above, it is recommended that the slits or the openings be formed so that the center distance h between the center position of the agitator in the direction at right angle to the rotary shaft of the agitator and the center position of the plurality of slits in the direction at right angle to the rotary shaft of the agitator and the shortest distance H between the end portion of the agitator and the bottom of the toner reserve container satisfy a relationship of 0.5Hxe2x89xa6hxe2x89xa6H. The above-mentioned center position is determined as follows: for example, in the case of the slits, as shown in FIG. 1, taking into account only the plurality of slits 60xe2x80x94, if the number of slits 60 is an odd number, the center in the length L of the center slit 60c is the center position O, and the distance from the center position O to the center of the agitator 57 is the center distance h.
Then, the distance H is the shortest distance from the one end of the agitator 57 to the bottom of the inside wall of the toner reserve container 50, as shown in FIG. 2. If the plurality of slits or openings are formed in the conveying sheet with respect to the center position O in the relationship between the center distance h and the distance H, as described above, the conveying sheet can secure good toner conveyance and keep the stable toner conveyance for a long time.
Also, in the toner replenishing device in accordance with the second invention described above, the toner conveyance depends, in particular, on the total area of the openings. In particular, if the total area of the openings increases, it naturally presents a problem of the rigidity of the conveying sheet and the like, and if it is small, the conveying sheet can not be easily deformed to be plastically deformed. For this reason, if the plurality of openings are formed so that the opening ratio Sr of the total opening area Sk of the plurality of openings to the total area Ss of the conveying sheet (Sr=Sk/Ssxc3x97100%) is set at a range from 10% to 30%, the conveying sheet can keep good toner conveyance and perform stable, sufficient toner conveyance.
As described above, according to the present invention, if the slits or openings are simply formed in the conveying sheet constituting the toner conveying unit for the purpose of conveying the toner, which is provided in the toner replenishing device, it is possible to keep stable toner conveyance for a long time. Further, if the positions of the slits or the openings are suitably determined, it is possible to produce the better effect.